Lightweight, wearable and flexible supercapacitors (SCs) have generated acute interest for energy storage use due to their potential applications in wearable/roll-up display, electronic paper, mobile phone, sensor networks, hand-held portable devices and artificial electronic skin. SCs provide energy density greater than that of a conventional capacitor, with faster charge/discharge rates and a cycle life longer than that of batteries. A free-standing and binder-free electrode with robust mechanical strength and large capacitance is a vital factor for flexible SCs. As some of the most promising devices for energy storage, solid-state SCs have attracted intensive research interest because of their outstanding properties such as great safety, great flexibility, ultra-thin profile, high power density, light weight, and reduced environmental footprint, all of which offers great promise in the field of lightweight, portable, roll-up electronics. Solid-state SCs enable an entire device to be flexible, lightweight, thin, and compact, but, to fill the increasing energy demands for the next-generation portable electronic devices, the energy density of solid-state SCs must be further improved within confined areas or spaces. Conductive paper electrodes have attracted much interest for the development of planar wearable SCs. Cellulose paper is a general type of cheap and abundant material having outstanding flexibility. The porous and natural rough surfaces of paper are perfect for energy-storage devices, in which high surface roughness is advantageous for the handling of ions and electrons. Paper is an insulator, however, which presents limitations. To improve the conductivity of paper, carbon nanotubes can be coated on the surface of the paper with a solution-based method, but such method requires environmentally destructive chemicals and complicated processes, and carbon nanotubes remain prohibitively expensive.
This Discussion of the Background section is provided for background information only. The statements in this Discussion of the Background are not an admission that the subject matter disclosed in this Discussion of the Background section constitutes prior art to the present disclosure, and no conductive paper electrodes, electrochemical capacitors, or manufacturing methods described in this Discussion of the Background section may be used as an admission that any conductive paper electrode, electrochemical capacitor or manufacturing method of this application, including the conductive paper electrode, electrochemical capacitor and manufacturing method described in this Discussion of the Background section, constitutes prior art to the present disclosure.